Background: The International Commission on Radiological Protection (ICRP) has attributed the same relative risk for X and gamma radiations of all energies. Several studies have proven that the biological effect of low energy photon is more than that of higher ones. The assessment of risks is important due to the wide use of low energy X-rays for mammography screening and other diagnostic appli...

We estimate the energy distribution of positrons produced in interaction ultra-relativistic electrons with a high-intensity laser beam. The underlying trident process is factorized on probabilistic level. That is, we deploy two-step mechanism for formation electron-positron pairs. In first step, high-energy photon as result nonlinear Compton scattering. second an pair created by (multi-photon) ...

Absolute spectroscopic photocurrent calibration of detectors in the photon energy range of 50-6000 eV is performed at beamlines U3c and X8a of the National Synchrotron Light Source at Brookhaven National Laboratory. These beamlines are specifically designed to provide high flux over a wide energy range, with particular attention paid to harmonic purity of the monochromatic beam. Examples of opt...

Introduction: In clinical electron beams, most of bremsstrahlung radiation is produced by various linac head structures. This bremsstrahlung radiation dose is influenced by the geometry and construction of every component of the linac treatment head structures. Thus, it can be expected that the amount of the contaminated photon dose due to bremsstrahlung radiation varies among different linacs,...

I review the physics prospects for high energy photon photon colliders, emphasizing results presented at the LBL Gamma Gamma Collider Workshop. Advantages and difficulties are reported for studies of QCD, the electroweak gauge sector, supersymmetry, and electroweak symmetry breaking. This work was supported by the Director, Office of Energy Research, Office of High Energy and Nuclear Physics, D...

We report on the investigation of the photon energy dependence of double 1s photoionization of light atoms and compare the cross sections for hollow atom and He-like ion production. Measurements of the Kα hypersatellite x-ray spectra of Mg, Al, and Si were carried out using the Fribourg high-resolution x-ray spectrometer installed at the ID21 and ID26 beam lines at the ESRF. The double-to-singl...

OBJECTIVE Purpose of this work was to study the dose perturbation within the target volume of a external MV radiation therapy when using metal fiducials. METHODS We developed a Monte Carlo simulation in Geant4 of a cylindrical fiducial made either of gold or of steel and simulated the photon irradiation beam originating from a medical Linac operating at 6, 10 or 15 MV. For each energy, two di...

Background: Monte Carlo (MC) modeling of a linear accelerator is a prerequisite for Monte Carlo dose calculations in external beam radiotherapy. In this study, a simple and efficient model was developed for Elekta SL-25 linear accelerator using MCNP4C Monte Carlo code Materials and methods: The head of Elekta SL-25 linac was simulated for 6 and 18 MV photon beams using MCNP4C MC code. Energ...

We calculate photon production from a quark-gluon plasma which is anisotropic in momentum space including the Compton scattering, q(q̄) g → q(q̄) γ, and annihilation, q q̄ → g γ, processes. We show that for a quark-gluon plasma which has an oblate momentum-space anisotropy, 〈p2L〉 < 〈p 2 T 〉, the photon production rate has an angular dependence which is peaked transverse to the beam line. We propos...

A Monte Carlo model of an Elekta Precise linear accelerator has been built and verified by measured data for a 6 and 10 MV photon beam running with and without a flattening filter in the beam line. In this study the flattening filter was replaced with a 6 mm thick copper plate, provided by the linac vendor, in order to stabilize the beam. Several studies have shown that removal of the filter im...